1. Technical Field of the Invention
The present invention relates to a nuclear medicine diagnosis equipment, and particularly, to a gamma ray detector and a gamma ray reconstruction method for use in SPECT and PET.
2. Description of the Related Art
The gamma ray detector is a radiation detector and is an equipment used in nuclear medicine diagnosis for measuring gamma rays (γ rays) emitted from radioactive medicines given to a patient.
A conventional radiation detector is a laminate of a collimator, a NaI (sodium iodide) and a PMT (photomultiplier tube), in which a lead collimator with parallel micro-pores allows only gamma rays coming from the direction of the pores to reach single crystals of the NaI, whereby fluorescent light is emitted proportional to the amount of gamma ray energy deposited therein, and the PMT detects the light to detect the intensity and the position of the gamma rays.
SPECT is an abbreviation for single photon ECT (ECT stands for emission computed tomography), and is an equipment that creates scintigrams (detection images of a radiation detector) from the directions surrounding a patient using single photon nuclides, thereby obtaining the cross-sectional distribution of radioactive medicines.
Moreover, PET (positron emission tomography) is an abbreviation for positron ECT and is an equipment that uses radioisotopes emitting positrons during decays to successively detect two photons flying out in opposite directions when the positrons combine with electrons, using two detectors, thereby calculating the incidence direction of gamma rays and creating tomographic images.
In relation to the above-described radiation detector used in SPECT and PET, proposals have already been made, for example, in Patent Documents 1 and 2.
The invention of Patent Document 1 provides a universal SPECT/PET equipment that improves energy resolution without decreasing radiation collecting efficiency or spatial resolution, thereby improving the performance as SPECT equipment while maintaining the performance as PET equipment.
For this purpose, in the above invention, as illustrated in FIG. 1, radiation detectors 51 and 52 are respectively provided with semiconductor detector units 53a and 53b which are disposed close to radiation incidence surfaces 51a and 52a so as to absorb and detect gamma ray emission having energy of 140 keV, resulting from single photons, and scintillation detector units 54a and 54b which are disposed on opposite sides to the radiation incidence surfaces 51a and 52a with the semiconductor detector units 53a and 53b disposed between them so as to detect gamma ray emission having energy of 511 keV, resulting from positrons.
The invention of Patent Document 2 provides a radiation detector that improves the spatial resolution of a positron emission tomography (PET) equipment attached with a radiation detector so that sensitivity thereof is not decreased.
For this purpose, in the above invention, as illustrated in FIG. 2, sixty-four scintillators 61 are closely coupled to construct a scintillator array 62, and respective scintillators 61 are optically coupled to an APD array 64 comprising sixty-eight avalanche photodiodes (APD) 63 which correspond to the scintillators 61 in an one-to-one relation. Gamma rays incident on the scintillator array 62 emit light from scintillators corresponding to the absorbed positions through an interaction, and the emitted light is diffused to neighboring scintillators and the light intensity is detected by the respective APDs 63 of the APD arrays 64. The detection data which are detected by the respective APDs 63 and subjected to photoelectric conversion are input to an incident position calculation circuit 65, whereby the center of the light intensity distribution is calculated based on the respective detection data and then the incident positions of the gamma rays are obtained.